EC 19529-4430: SALT identifies the most carbon- and metal-poor extreme helium star
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866916194996453376 |
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| author | Jeffery, Simon Scott, Laura Monai, Asish Philip Miszalski, Brent Woolf, Vincent |
| author_facet | Jeffery, Simon Scott, Laura Monai, Asish Philip Miszalski, Brent Woolf, Vincent |
| contents | EC 19529-4430 was identified as a helium-rich star in the Edinburgh-Cape Survey of faint-blue objects and subsequently resolved as a metal-poor extreme helium (EHe) star in the SALT survey of chemically-peculiar hot subdwarfs. This paper presents a fine analysis of the SALT high-resolution spectrum. EC 19529-4430 has $T_{\rm eff} = 20\,700 \pm250$\,K, $\log g /{\rm cm\,s^{-2}} = 3.49\pm0.03$, and an overall metallicity some 1.3 dex below solar; surface hydrogen is $\approx 0.5\%$ by number. The surface CNO ratio 1:100:8 implies that the surface consists principally of CNO-processed helium and makes EC 19529-4430 the coolest known carbon-poor and nitrogen-rich EHe star. Metal-rich analogues include V652 Her and GALEX J184559.8-413827. Kinematically, its retrograde orbit indicates membership of the galactic halo. No pulsations were detected in TESS photometry and there is no evidence for a binary companion. EC 19529-4430 most likely formed from the merging of two helium white dwarfs, which themselves formed as a binary system some 11 Gyr ago. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2404_03972 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | EC 19529-4430: SALT identifies the most carbon- and metal-poor extreme helium star Jeffery, Simon Scott, Laura Monai, Asish Philip Miszalski, Brent Woolf, Vincent Solar and Stellar Astrophysics Astrophysics of Galaxies EC 19529-4430 was identified as a helium-rich star in the Edinburgh-Cape Survey of faint-blue objects and subsequently resolved as a metal-poor extreme helium (EHe) star in the SALT survey of chemically-peculiar hot subdwarfs. This paper presents a fine analysis of the SALT high-resolution spectrum. EC 19529-4430 has $T_{\rm eff} = 20\,700 \pm250$\,K, $\log g /{\rm cm\,s^{-2}} = 3.49\pm0.03$, and an overall metallicity some 1.3 dex below solar; surface hydrogen is $\approx 0.5\%$ by number. The surface CNO ratio 1:100:8 implies that the surface consists principally of CNO-processed helium and makes EC 19529-4430 the coolest known carbon-poor and nitrogen-rich EHe star. Metal-rich analogues include V652 Her and GALEX J184559.8-413827. Kinematically, its retrograde orbit indicates membership of the galactic halo. No pulsations were detected in TESS photometry and there is no evidence for a binary companion. EC 19529-4430 most likely formed from the merging of two helium white dwarfs, which themselves formed as a binary system some 11 Gyr ago. |
| title | EC 19529-4430: SALT identifies the most carbon- and metal-poor extreme helium star |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2404.03972 |